While it’s not a direct necessity to have this knowledge in order to create a good, usable design, understanding the medium used to bring your ideas to life can still be beneficial for UX and UI designers’ work. It helps you think differently, makes you a better communicator, a better collaborator and adds a skill to your resume.
Building a website is not just about deciding how it’s going to look, how it’s going to function, or what content it’s going to contain. You also have to decide how you’re actually going to build it. When building a website, you have 2 general directions you can choose from: hand code or use a content management system (CMS). There are pros and cons to both directions so one is not necessarily better than the other. You must evaluate your situation and decide which one works best for your needs.